Hydraulic transmission



Jan. 7, 1936- I n J. K. DOUGLAS 2 ,7

HYDRAULIC TRANSMISSION Filed July 9, 1934 INVENTEIR JAMES K.D DUELAS Patented i... 7, 1936 UNITED STATES PATENT OFFICE 'The'oilgear Company, Milwaukee,

- poration of Wisconsin Wis., a cor Application July 9, 1934, Serial No. 734,326

, 19Claims.

This invention relates to hydraulic transmlssions of the type employed to move a tool or a piece of work atdifl'erent rates during different parts of a cycle of operation.

In certain operations, such as drilling, it is desirable to feed the tool through the work at a given rate and then, at a certain point in the operation, suddenly reduce the feed rate. For example, a drill should be fed through the work at the highest practicable rate in order to obtain maximum production from the drilling machine but, if the high feedrate is maintained after the point of the drill breaks through the work, the drill .will usually lunge forward and thread itself through the remaining portion of the metalwhich is too strong to be torn away from the edges of the hole by the drill, thereby causing the drill to break or to stall.v Q

The present invention has as an object to provide a hydraulic transmission in which the motor will operate at a relatively fast rate as long as the work performed by it causes the pump to create a pressure above a given value and will have its rate of operation. automatically reduced upon pump pressure falling below that value.

Another object is to provide a hydraulic transmission in which the motor will operate at one speed when pressure exceeds a certainvalue and at a lower speed when pump pressure falls below that value, and in which" each of those speeds is maintained within close limits.

Another object is to provide a hydraulic transmission of thischaracter which is positive and precise in operation.

7 Another object is to provide a hydraulic transmission with an automatic displacement varying mechanism which is simple in construction and which may be readily and accurately adjusted.

Other objects and advantages will appear from the description hereinafter given of a hydraulic transmission in which the invention is embodied.

According to the invention in its general aspect,

' the transmission has its pump provided with a ing the displacement varying element toward zero displacement position when pump pressure draulic motor I, a pump 2 for supplying liquid to the motor, mechanism 3 for varying pump displacement, a valve 4 for controlling the flow of liquid to and from the motor, and suitable fluid channels connecting the valve to the motor and to the pump.

The motor is shown as being of the ordinary reciprocating type and as having its cylinder fastened to the frame 5 of a drill press. The motor cylinder has a piston 6 fitted therein and provided with a piston rod 1 which is connected to the spindle 8 of the drill press through an antifriction thrust bearing 9 to permit the spindle to rotate without rotating the rod I or the piston 6.

The spindle 8 is rotated by a belt In which engages a pulley H fixed upon the spindle inside a bearing l2 carried by the frame 5.

The drill press is provided with a work table I3 to support a piece of work 14 which is to be operated upon by a drill .15 fastened to the spindle 8 to rotate therewith.

,The pump 2 is of a well known type and a description or a detailed illustration thereof is not necessary to an understanding of the present invention. It is suificient to state that the pump has its cylinders arranged radially in a cylinder barrel [6 and its pistons in contact with the an- 3 nular inner surface of an adjustable thrust member H. The cylinder barrel ordinarily rotates at a constant speed upon a stationary valve shaft or pintle l8 through which liquid flows to and from the cylinders. The displacement of the pump, and consequently the rate at which the drill I5 is advanced into the work It, depends upon the distance which the axis of the thrust member I1 is offset from the axis of the pintle [8.

When the axis of the thrust member I1 coincides with the axis of the cylinder barrel, the pump is at zero stroke and no liquid will be delivered thereby. When the axisof the thrust member is moved to one side of the axis of the cylinder barrel, the pump will deliver liquid at a rate dependent upon the distance=between the axes. If it is moved above the cylinder barrel axis as shown in the drawing, the pump will deliver liquid into a discharge pipe I 9 and liquid will flow into the pump cylinders through a return pipe 20.

The pipes 9 and 20 have one end of each connected to the pintle I8 and the other end of each connected to the valve 4 which is connected by pipes 2| and 22 to opposite ends of the motor I to control the operation thereof.

In the-arrangement shown, the volume of liquid delivered into the pipe I 9 is sufiicient only for operating the motor at limited speeds, that is, at speeds suitable for feeding the drill into'and through the work, but the pump ordinarily has a larger capacity gear pump incorporated therein or associated therewith for driving the motor at' rapid traverse speed. The valve 4 controls the delivery of liquid to the motor from both of the.

pumps. Since the gear pump forms no part of the present invention, it has beenomitted from the drawing in order to simplify the 'same."

The thrust member I1 is urged toward maximum displacement position by 'two springs 23 which have suflicient strength to support the thrust member l1 and to move it upward when shaft in the opposite direction. will permit the springs 23 to move the thrust member I1 upward and thereby increase pump displacement.

All power pumps have as an inherent characteristic thereof an internal leakage or slip which varies directly in accordance with variation in pump pressure. In order to compensate for this variation in slip, the thrust member i1 is ordinarily urged by a force proportional to pump .pressure toward maximum displacement position against the resistance of spring means which yields as pump pressure increases.

As shown, the thr ust member I1 is urged upward by afluid actuated plunger 26 against a spring 21." The plunger 26 is fitted in a stationary cylinder 28 which is connected to the discharge pipe I!) by a pipe 29 so that the plunger 26 is subjected at all times to pump pressure. The spring 21 is shown as consisting of, a stackof Belleville-spring washers arranged in a socket 30 which is carried by the thrust member l1 and has a plunger 3| fitted therein and normally in contact with both the spring 21 and the cam 24. r

' When the pump is delivering liquid, the thrust member I1 is urged upward by the plunger 26 with a force proportional to pump pressure, and it is'also urged upward by the springs 23. As pumppressure increases and causes an increase in slip, the foroe'exerted by the plunger 26 increases and compresses the spring 21 slightly, thereby increasing pump displacement by an amount'which is just sufficient to compensate for.

the increase in'slip. The thrust member I1 is urged downward by the displacement varying mechanism 3. This mechanism is provided with an internally threaded socket 32 which is carried by the pump casing in 'alinement with the plunger 3| and has an externally threaded cylinder 33 threaded therein. The cylinder 33 is provided at its lower end with an annular flange 34' which functions as a stop to limit the distance through which the thrust mem her I 1 may be moved by the displacement varying mechanism 3.

The cylinder 33 has threaded therein an externally threaded cylinder 35which is closedat its upper end by an adjusting knob 36. A helical compression spring 31 is arranged inside-the cylinders 33 and 35 with its upper end in contact with the underside of the knob 36 and its lower end in contact with a push pin 38 which extends downward through the socket 32 and has its head 39 arranged inside the cylinder 33 in contact with the spring 31 and overlapping the flange 34. The spring 31 transmits a downward pressure upon the thrust member l1 through a bifurcated pressure member 43 which straddles the control shaft 25 and has its upper endin contact with the push pin 38 and its lower end in contact with the plunger 3|.

The spring 31 tends to move the thrust member |1 downward and thereby cause the pump to deliver liquid at a rate lower than the rate determined by the adjustment :of the cam 24, but when the pump isdelivering liquid at a'pressufe above a predetermined value, the upward force exerted by the plunger 26 added to the upward force exerted by the springs 23 exceeds the downward force exerted by the spring 31 and holds the plunger 3| in contact with the cam 24 to cause the pump to deliver liquid at the predetermined fast feed rate.

When pump pressure falls below the predetermined value, the downward force exerted by the spring 31 overcomes the upward forces exerted by the plunger 25 and the springs 23 and moves the thrust member downward until the head 39 of the pin 38 engages the flange 34, thereby causing the pump 'to deliver liquid at a slow feed rate determined by the position of the flange 34.

The pump pressure, at which the pump will automatically change from one feed rate to the other,'- is determined by the tension of the spring 31 which may be adjusted by turning the knob 36 to vary the distance between its underside and the head 39 of the pin 38. This pressure may be indicated by suitable graduations cut into the unthreaded surface of the cylinder 35 at 4| to register with the top of the cylinder 33.

The slow feed rate is determined by the position of the flange 34 which limits-the downward movement of the pin 38 and, consequently, the downward movement of the thrust member l1. This feed rate may be indicated by suitable graduations cut in the unthreadedssurface of the cylinder 33 at 42 to register with the top of the socket 32. The position of the flange 34 may be adjusted by turning the cylinder 33 which, for this purpose, has an annular adjusting knob 43 fixed to its upper end.

The knob 43 may be turned to adJust the pump to the exact slow. feed rate desired and then held stationary while the knob 36 is turned to" adjust the spring 31 to the exact tension required to a cause the pump to change from fastfeed rate to slow feed rate at the instant that pump pressure drops to a predetermined valuebut, in the majority of installations, it is desirable to keep the reading on the gradulations 4| unchanged when adjusting the slow feed rate of the pump. Consequently, the knob 43 is ordinarily provided with a spring detent 44 which engages the cylinder 35 and causes 'it to turn in unisonwith the cylinder 33. p

In the majority of variable displacement pumps employed for operating the feed mechanisms of machine tools, a slight, variation in the length rate.

, of the stroke .of the pump will cause a relatively pressure falls below said value to thereby cau e large variation in the volumetric delivery of the pump. For example, if the thrust member I] should be moved slightly, pump output will be varied considerably. Consequently, only a slight axial movement of the cylinder 33 is necessary to make a considerable variation in the slow feed This axial movement is so slight that, if the spring- 31 is relatively long as shown in the drawing, the cylinder 35 may turn with the cylinder 33 and cause only a slight'variation in the tension of the spring 31 and, therefore, only a slight variation in the pressure at which the pump will change from fast feed rate to slow. feed rate.

When the drill I5 is advanced into contact with the work M, the resistance of thework to the entry of the drill point causes pump pressure to rise sufliciently to enable the plunger 26 to move the thrust member ll upward until the plunger 3! engages the cam 24. The drill will then be fed into the work at a substantially uniform fast feed rate'which is; determined by the adjustment of the cam 24.

If the resistance of the work should be such as to cause pump pressure to rise still higher and thereby cause the slip of the pump to increase,

the spring washers 21 will yield slightly under the additional force exerted by the plunger 26 due to the increase in pumppressure, thereby permitting the thrust member I! to move upward and-increase pump delivery by an amount substantially equal to the increase in slip, Thedrill is thus fed into the work at a fast feed rate which remains substantially constant as long as the drill meets suflicient resistance.

When the drill has so nearly completed its operation that only a thin shell of metal remains under it, this thin shell will yield under the thrust of the drill and cause pump pressure to' drop, thereby decreasing the upward force exerted by the plunger 26 upon the thrust member I1 and enabling the spring 31 to move the thrust mem-' her I? downward and cause the pump to deliver liquid to the motor I at the, slow feed rate determinedby the position of the flange 34. Thedrill is then advanced slowly through the remaining part of the work without danger of damage to the drill or to the machine. The drawing shows supplying liquid to said motor and having an element movable to vary pump displacement and thereby vary the speed of said motor, fluid operated means responsive to pressure created by said pump for moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction,

and other means for moving said element; in a said pump to operate said motor at a lower rate of speed.

2. A hydraulic transmission, comprising a hydraulic motor, avariable displacement pump for supplying liquid to said motor and having an element movable to vary. pump displacement and thereby vary the speed of said motor, fluid operated means responsive to pressure created by said pump for moving said element in a direction to increase pump delivery, a stop for glimiting the movement of said element in said direction, 'other means for moving said element in a direction to decrease pump delivery, and an abutment for limiting the, extent of movement of said element by said other means; said other means being yield-,

able under the action of said fluid iiperated means when pump pressure exceeds a' predetermined value to thereby enable said pump to operate said motor at a rate of speed limited by said stop and said other'means beingcapable of moving said means when pump pressure falls below said value to thereby cause said' pump to operate said motor at a lower rate of speed, but not less than the rate. determined by the position of said abutment.

3. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump for supplying liquid to said motor and having an element movable to vary pump displacement and thereby vary the speed of said motor, fluid operated means responsive to pressure created by said pump for moving said element in a direction to increase pump delivery, a stop for limiting the movementof said element in said direction, other means for moving said element in a direction to decrease pump delivery; said other means being H said motor at a lower rate of speed, and means operable when pump pressure exceeds said predetermined value for compensating for variations in the slipof said pump.

4. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump for supplying liquid to said motor and having an element movable to vary pump displacement and thereby vary the speedof said motor, fluidoperated means responsive to pressure created by said pump for moving said element in a direction to increase pump delivery. a stop for limiting the movement of said element in said direction, other means. for moving said element in a direction to decrease pump delivery. and an abutment for limiting the extent of movement of said element element against the action of said fluid operated by said other means; said other means being yieldable under the action of said fluid operated means when pump pressure exceeds a predetermined value to thereby enable said pump to opera-e said motor at a rate of speed limited by said stop and said other means being capable of mcving said element againstthe action of saidfluid operated means when pump pressure falls belew said value to thereby cause said pump to operate said motor at a lower rate of speed, but not less than the rate determined by theposition of said abutment, and means operable when pump pro:-

sureexceeds said predetermined value for com- ,draulic motor, a variable displacement pump for supplying liquid to said motor and having an ele-' Cir pensating for variations in the slip of said pump.

5."A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump for supplying liquid to said motor and having an element movable to vary pump displacement and thereby vary the speed of said motor, fluid operated means responsive to pressure created by said pump for moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction, other means for moving said element in a direction to decrease .pump delivery; said other means being yield-able under the action of said fluid operated means when pump pressure exceeds a predetermined value to thereby enable said pump to operate said motor. at a rate of speed limited by said stop and said other means being capable of moving said element against the action of said fluid operated means when pump pressure falls below said value to thereby cause said pumpto operate said motor at a low'er rate of speed, and spring means arranged between said element and said stop for compensating for variations in the slip of said pump during periods in which pump pressure exceeds said predetermined value.

6. A hydraulic transmission, comprising a hyment movable to vary pump displacement and thereby vary the speed of said motor, fluid perated means responsive to pressure created by said pump for moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction, other means for moving said element in a direction to decrease pump delivery, an abutment for limiting the extent of movement of said element by said 'other means; said other means being yieldable under the action of said fluid operated means when pump pressure exceeds a predetermined value to thereby enable said pump to operate said motor at a rate of speed limited by said stop and said other means being capable of moving said element against the action of said fluid operated means when pump pressure falls below said value to thereby cause said pump to operate said motor at a lower rate of speed, but not less than the rate determined by the position of said abutment, and spring means arranged between said element and said stop for compensating for variations in the slip of said pump during periods in which pump pressure exceeds said predetermined value.

7. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump connected to said motor for operating the same and provided with a displacement varying element, fluid operated means responsive to pump pressure for moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction, a plunger for moving said element in the opposite direction to decrease pump delivery, and a spring acting independent of said stop for urging said plunger toward said element and adapted to yield under the action ,of said fluid actuated means when pump pressureexceeds a' predetermined value and to move said element against the action of. said fluid operated means when pump pressure falls .below said value.

' '8. A hydraulic'transmission, comprising a. hydraulic motor, a variable displacement pump connected to said motor for operating thesame and -;-.provided with a displacement-varyin element, (fluid operated means responsive to pump pressure for moving said element in a direction to increase pump delivery, a stop for. limiting the movement of said element in said direction, a

plunger for moving said element in the opposite direction to decrease pump delive y, a spring acting independent of said stop for urging said plunger toward said element and adapted to yield under the action of said fluid actuated means when pump pressure exceeds a predeter mined value and to move said element against the action of said fluid operated means when pump pressure falls below said value, and means for limiting the movement of said element in a direction to reduce pump delivery. 9. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump connected to said motor for operating the same and provided with a displacement varying element, fluid operated means responsive to pump pressure for moving said element in a direction to in-- crease pump delivery, astop for limiting the movement of said element in said direction, a plunger for moving said element in the opposite direction to decrease pump delivery, a spring acting independent of said stop for urging said plunger toward said element and adapted to yield under the action of said fluid actuated means when pump pressure exceeds a predetermined value and to move said element against the action of said fluid operated means when pump pressure falls below said value, and means arranged between said stop and said element for compensating for variations in pump delivery due to variations in pump pressure above a predetermined pressure.

10. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump connected to said motor for operating the same and provided with a displacement varying element, fluid operated means responsive to pump pressure ior moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction, a plunger for movingsaid element in the opposite direction to decrease pump delivery, a spring acting independent of said stop for urging said plunger toward said element and adapted to yield under the action of said fluid actuated means when pump pressure exceeds a predetermined value and to move said element against the action of said fluid operated means when pump pressure falls below said value, means for limiting the movement of said element in a direction to reduce pump delivery, and means arranged between said stop and said element for compensating for variations in pump delivery due to variations in pump pressure above a predetermined pressure.

11. A hydraulic transmission, comprising a hydraulic motor, avariable displacement piunp connected to said motor for operating the same and to yield under the action of said fluid operated means when pump pressure exceeds a predetermined value and to move said element against the action of said fluid operated means when 12. A hydraulic transmission, comprising a hydraulic motor, 'a variable displacement pump connected to said motor for operating the same and provided with a displacement varying element, fluid operated means responsive to pump pressure for moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction to thereby limit the maximum output of said pump, a plunger for moving said element in the opposite direction 'to decrease pump delivery, a stationary support, a spring retainer carried by said support, and a spring arranged within said retainer for urging said plunger toward said element and adjustable as to tension by adjustment of said retainer, said spring being adapted to yield under the action of said fluid operated means when pump pressure exceeds a predetermined value and to move said. element against the action of said fluid operated means when pump pressure falls below said predetermined value.

13. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump connected to said motor for operating the same and provided with a displacement varying element, fluid operated means responsive to pump pressure for moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction to thereby limit the maximum output of said pump. a plunger for moving said element in the opposite direction to decrease pump delivery, a stationary support, a spring retainer carried by said support, a spring arranged within said retainer for urging said plunger toward said element and adjustable as to tension by adjustment of said retainer,

said spring being adapted to yield under the action of said fluid operated means when pump pressure exceeds a predetermined value and to move said element against the action of said fluid operated means when pump pressure falls below said predetermined value, and means carried by said retainer for limiting the movement of said plunger to thereby limit the reduction in pump delivery.

14. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump connected to said motor for operating the same and provided with a displacement varying element, fluid operated means responsive to pump pressure for moving said element in a direction to increase pump delivery, a stop for limiting the movementof said element in said direction to thereby limit the maximum output of said pump, a plunger for moving said element in the opposite direction to decrease pump delivery, a stationary support, a cylinder threaded into said support and provided with an abutment to limit the movement of said plunger whereby rotation of said cylinder in said support will vary the distance said plunger can move said element, a spring arranged within said cylinder for urging said plunger toward said element, and a second cylinder threadedinto said first cylinder 'where-' .by rotation of said second cylinder will adjust the tension of said spring, said spring being adapted to yield under the action of said fluid operated means when pump pressure exceeds a predetermined value and to move said element against the action of said fluid operatedmeans when pump pressure falls below said mined value.

15. A hydraulic transmission, comprising a predeterv the movement of said element in said direction to thereby limit the maximum output to said pump, spring means arranged between said 'stop and said element for compensating for variations 1 in the slip of said pump due to variations inpump pressure above a predetermined pressure,

a plunger acting through said spring means for moving said element in the opposite direction to decrease pump delivery, and a spring'acting in- 15 dependent of said stop for urging said plunger toward said element and adapted to yield under the action of said fluid operated means when pump pressure exceeds a predetermined value and to move said element against the action of 20 said fluid operated means when pump pressure falls below said predetermined value.

16. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump connected to said motor for operating the same 25 and provided with a displacement varying element, fluid operated means responsive to pump pressure for moving said element in a direction to'inorease' pump delivery, a stop for limitin. the movement ofsaid element in said direction 30 to thereby limit the maximum output of said pump, spring means arranged between said stop and said element for compensating for' variations in the slip of said pump due to variations in pump pressure above a predetermined pressure, 35 a plunger acting through said spring means for moving said element in the opposite direction to decrease pump delivery, a stationary support, a spring retainer carried by said supportand a spring arranged within said retainer for urging 40 said plunger toward said element and adjustable as to'tension by adjustment of said retainer, said spring being adapted to yield under the action of said fluid operated means when pump pressure exceeds a predetermined value and to move 5 said element against the action of said fluid, operated means when pump pressure falls belo said predetermined value.

17. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump 50 connected to said motor for operating the same and provided with a displacement varying element, fluid operated means responsive to pump pressure for moving said element in a direction to increase pump delivery, a stop for limiting the movement of said element in said direction to thereby limit the maximum output of said pump, spring means arranged between said stop and said element for compensating for variations in the slip of said'pump due to variations in pump pressure above a predetermined pressure,

a plunger acting through said spring means for moving said element in the opposite direction to decrease pump delivery. a stationary support, a spring retainer carried by said support, a spring 5 arranged within said retainer for urging said plunger toward said element and adjustable as 'said predetermined value; and means carried by said retainer for limiting thmmovementof said 7 plunger to thereby limit the reduction in pump delivery.

l8. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump connected to said motor for operating the same and provided with a displacement varying 'element, fluid operated means responsive to pump pressure for moving said element in a direction to increase pump delivery, a stop for limiting the movement of'said element in said direction to thereby limit the maximum output of said pump, spring means arranged between said stop and said element for compensating for variations in 1 the slip of said pump due to variations in pump pressure above a predetermined pressure, a plunger acting through said spring means for moving said element in the opposite direction to decrease pump delivery, a stationary support,

a cylinder threadedinto said support and provided with an abutment to limitthe movement of said plunger whereby rotation of said cylinder in said support will vary the distance said plunger can move said element, a spring arranged within said cylinder for urging said plunger toward said element, and a second cylinder threaded into. said first cylinder whereby rotation ofvsaid second cylinder will adjust the tension of said spring, said-spring being adapted to yield under the action of said fluid operated means when pump pressure exceeds 'a predetermined value and to move said element against the action of said fluid operated means when pump pressure falls below said predetermined value.

19. A hydraulic transmission, comprising a hydraulic motor, a variable displacement pump for supplying liquid to said motor and having an elementmovable to vary pump displacement and thereby vary the speed of said motor, pressure and discharge channels connecting said pump to said motor, a fluid motor connected to I said pressure channel for moving said element in a direction to increase pump delivery in response to pressure created by said pump, a stop for limiting the movement of said element in said direction, and other means for moving said element in a direction to decrease pump delivery;

,. said other means being yieldable under the action of said fluid motor when pump pressure exceeds a predetermined value to thereby enable said pumpto operate said-hydraulic motor at a rate of speed which is limited by said stop and said other means being capable of moving said element againstthe action of said fluid motor when pump pressure falls below said value to thereby cause said pump to operate said hydraulic motor at a lower rate of speed.

JAMES K. DOUGLAS. 

